Mixer is widely applied in a communications system and capacitive touch system, and is configured to convert a high frequency received signal into a baseband signal, to facilitate further processing of the signal by a backend signal processing module. In general, the mixer implemented as a multiplier can generate a result of multiplying a received signal by a local signal. In addition, the mixer can be implemented by using a switching mixer, and the switching mixer has the advantages of high linearity, low noise and the like, and the switching mixer is controlled by a switch signal, wherein the switch signal has a switching frequency.
In the related art, in order to convert the high frequency received signal into the baseband signal, a switching frequency of the switch signal is generally the same as the frequency of the received signal. As such, the switching mixer can be equivalent to multiplying the received signal by a square wave having the same frequency as the received signal, and the square wave is the local signal. However, the square wave has relatively high sidelobes over the spectrum and harmonics at multiple frequency points, and the sidelobes and harmonics of the square ware would introduce additional noises, thereby reducing the signal to noise ratio (SNR) of the communications system or capacitive touch system.